Magnesium aluminum silicate phosphor



Nov. 22, 1960 F. A. HUMMEL 2,961,412

MAGNESIUM ALUMINUM sILcATE PHosPHoR Filed Aug. 2o, 1951' 560 580 @00 @zo 640 @e0 @a0 '700 i M90 M9422 04 lz 03 i 11m/@meter lbogd A-lummet, b9 HIS Acttto'neg.

United States Patent Oiice Patented Nov. 22, 1960 MAGNESIUM ALUMINUM SILICATE PHOSPHOR Floyd A. Hummel, State College, Pa., assignor to General Electric Company, a corporation of New York Filed Aug. 20, 1957, Ser. No. 679,316

2 Claims. (Cl. 252-301.4)

there; but the color of the emission may be diluted by the luminescence of the diluting component. For example, a composition lying between line AB and MgSiO3 or Mg2SiO4, which, of themselves, are red uorescing phosphors, will produce a red dluorescing mixture, the red component of which is a combination of the red band of the cordierite and the red band of the MgSiOa or of the Mg2SiO4; or if a composition lying below point A and toward the spinel (MgAl2O4) is prepared, the color of the emission of thelcomposition will be diluted with the red emission band of the cordierite and of the green emission band of the spinel.

The luminescent material according to the invention may be prepared by the solid state reaction of the magnesiuni oxide, aluminum oxide, and silicon dioxide, with l the addition of the manganese activator in the form of A further object of my invention is to provide an'imv proved phosphor having red emission of longer wavelength than the commonly used cathode-r-ay phosphors.

According to the invention, a magnesium aluminum silicate phosphor is activated by manganese and emits a deep red band when excited by cathode-rays.

The invention will best be understood when considered with the accompanying drawings, in which:

Fig. l compares the spectral distribution of the present phosphor with known cathode-ray phosphors; and,

Fig. 2 is a phase diagram illustrating possible compositions of the instant phosphor.

A manganese-activated magnesium aluminum silicate phosphor according to the present invention is illustrated by curve A. Curve B is `a known manganese-activated magnesium silicate which emits in the red region when excited by cathode-ray radiation. Curve C is a manganese-activated zinc phosphate phosphor, which is also a red-emitting phosphor under cathode-ray excitation. The manganese-activated zinc phosphate phosphor is a known phosphor and is the material presently being widely used as the red component in color television tubes. The deeper red of the magnesium silicate according to the present invention makes it desirable as the red component in color television tubes; it may, however, be used Ifor a variety of other purposes such as color correction.

Referring to Fig. 2, there is illustrated a phase diagram between magnesium oxide (MgO), aluminum oxide (A1203), and silica or silicon dioxide (SiOZ). The phosphor matrix according to the present invention is illustrated by the line AB; the lower limit being composed of 2MgO'2Al2O3-5Si02 and the upper limit being composed of 2MgO2Al2O38SiO2. The lower limit of 2MgO-2Al2O35SiO2 is the natural occurring mineral cordierite. Cordierite forms solid solutions with silica up to a molecular ratio of 2MgO-2Al2O3-8Si02. In this solid solution from A to B, the same crystal produces luminescence when properly activated. Any deviation from line AB Will still result in the characteristic red component of cordierite but such luminescent emission of cordierite will be diluted with the emissions of other materials. lConcerning the ternary system MgOAl2O3SiO2, cordierite can be made to appear in many compositions surrounding the composition represented by line AB. If compositions oi the line joining cordierite and silica are prepared, one will expect to get SiO2 (silica), MgAlzO., (spinel), Mgzslob 3A12032S102 (munite), 0f A1203 (corundum, naturally occurring aluminum oxide) as associated phases. Therefore, on any composition off line AB, the red component of cordierite will still be manganese carbonate (MnCO3), or other well-known manganese salts preferably of the type which decomposes on heating into a halide or oxide and a volatile gas, for example, manganese nitrate, sulphate or acetate. The mixture is then fired between 1200o C. and 1400a C., the temperature range of about l325 C. to 1375 C. appears to be optimum where no ux is used. The firing, where no flux is used, is conducted for at least four hours; firing in excess of about two hundred hours does not appearto have any added advantage. It has been found, however, that the temperature and firing time can be 'appreciably reduced by the addition of a ux such as magnesium uoride .(MgFz). Magnesium uoride flux can be used in the range of about 0.05 mole to 0.5 mole per 2 moles of MgO in the matrix composition of the final phosphor; with about 0.2 mole of magnesium fluoride flux giving satisfactory effective results. With the addition of the ux, firing may be as short as one hour at a temperature in the range of 1200" C. to 1300J C.; firing for two hours appears to produce satisfactory results, but longer firing time may give a slightly more efficient phosphor; there appears to be no added advantage in firing for more than about two hundred hours.

Specific examples for the preparation of the phosphor according to the invention -are as follows:

(l) The following ingredients are combined in the solid state:

66.5 gm. MgO' 12.5 gm. MgFz (Flux) 18.5 gm. MnCO3 (44.5% Mn) gm. A12O33H2O 339 gm. SOZ'XHZO (13% H2O) This is essentially equivalent to 1.65 moles of MgO, 0.2 mole of MgFz, .15 mole of MnCO3, 2 moles of wherein 0.15 mole of the magnesium have been replaced by manganese. While the manganese constitutes the activator for the cordierite, it is in the form of manganese oxide as the manganese is merely substituted for the magnesium.

(2) Without the addition of a rflux to promote the reaction, the luminescent material may be prepared by combining the following ingredients:

36 gms. MgO

12.32 gm. MnCO3 (44.5% Mn) 156 gm. A12O33H2O 177.5 gm. sio2-XH2o (13% H20) 24.9 gm. MgF2 (Flux) 24.6 gm. MnCO3 (44.5% Mn) 56.4 gm. MgO

542 gm. SiOz-XHZO (13% H2O) This is esentially `equivalent to 0.4 `mole of MgF2, 0.2 mole MnCO3, 1.4 moles MgO, 2 moles A12O33H2O and 8 moles SiO2XH20. The mixture is tired the same as Example 1 above.

As previously stated, the optimum matrix is along line AB in the phase diagram with a yquantity of the magnesium replaced by manganese activator. -If the luminescent material is represented by the equation 4 XMgO-YAl2O3-ZSiO2:AMnO, a satisfactory red fluorescent phosphor may be obtained where X-l-A is in the range of 1.8 to 2.2; Y is in fthe range 1.8 to 2.2; Z is in the range of 4.8 to 8.2; and A is in the range of 0.07 to 0.4. A=0.2 mole appears to give optimum results; more than 0.4 mole of manganese oxide appears to reduce the brightness of the luminescent material.

It can be seen that many modifications can be made, for example, the phosphor in Examples 1 and 3 does not need 'to be retired; the manganese activator may be added as other salts of manganese; and the ratio of the compositions may be in a wide range. VThe invention, therefore, is to be limited only by the claims annexed to and forming a pant of this specification.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A luminescent material having essentially the formulae XMgOYAl2O3-ZSiO2:AMnO wherein X-l-A is in the range of 1.8 to 2.2, Y is inthe range of 1.8 to 2.2, Z Vis in the range of 4.8 to 8.2, and A is in activator proportions in the range of about 0.07 to 0.4.

2. A luminescent material having essentially the formulae XMgOYAl2O3-ZSiO2zAMnO wherein X-lA is about 2, Y is about 2, Z is in 'the range of about 5 to 8, and A is about 0.2.

References Cited in the le of this patent UNITED STATES PATENTS 2,141,905 Fonda Dec. 27,- 1938 2,254,956 Aschermann Sept. 2, 1941 2,257,667 Aschermann Sept. 30, 1941 2,308,736 Aschermann Ian. 19, 1943 

1. A LUMINESCENT MATERIAL HAVING ESSENTIALLY THE FORMULATE XMGO.YAL2O3.ZSIO2:AMNO WHEREIN X+A IS IN THE RANGE OF 1.8 TO 2.2, Y IS IN THE RANGE OF 1.8 TO 2.2, Z IS IN THE RANGE OF 4.8 TO 8.2, AND A IS IN ACTIVATOR PROPORTIONS IN THE RANGE OF ABOUT 0.07 TO 0.4. 